David,
I see what you mean when you say that this is a grey area in XSD. I checked
the Recommendation and indeed this is a grey area. It is true that the
current CIQ schema does not violate any normative statement in the
Recommendation. So even though it is intuitively wrong, it is not an
outright error either.
The reason I say it is intuitively wrong is that *actually* extending a
"complex type definition with simple content" into a "complex type
definition with complex content" (i.e., by adding particles) is forbidden by
the Recommendation. So you cannot use the <complexContent> tag for the only
purpose for which this tag exists--that is, to specify complex content.
However, you are allowed to use that tag (as an alternative to
<simpleContent>) **so long as it has no effect**, which is funny!
Notice that in this case the resulting (extended) type will be a complex
type with **simple** content, even though the tag <complexContent> is being
used. It feels wrong, doesn't it?
Alessandro